The Audio Pages

Category Index of Projects
Page Last Updated - August 2024

Main Index Projects Index Project List Pricelist

No.	'Special'	Description	Date	Flags
00	Opamp Bypassing	How (and why) to apply bypass caps to audio circuits using opamps and/or discrete circuitry (A 'must read' article)	2023
No.	Power Amplifiers & Accessories	Description	Date	Flags
03	60W / 8 Ohm Power Amplifier	My old faithful power amp design - For the latest (and much better version), see Project 3A	2007
10	20 Watt Class-A Power amp	True Class-A power amp for low power systems or tri-amping	2000
12	Simple Current F/B Amp	An update of a very old 60W / 8 Ohm design (formerly incorrectly referred to as 'El-Cheapo'	2012
12a	El-Cheapo	This is the real El-Cheapo - presented more or less as originally published (1964).  30W / 8 Ohm design	2012
19	Single Chip 50W Power Amplifier	Using the National Semiconductor LM3876 Power IC.
23	Power Amp Clipping Indicator	A fast and accurate indicator to show an amp is clipping (Updated)	2005
33	Loudspeaker Protection & Muting	Protect speakers from turn-on and turn-off transients and amplifier faults.  (See important updates to this project)	2007
36	Death Of Zen (DoZ)	An ultra simple, high performance Class-A power amp.  A lot of people have now built this amp, and all seem very pleased.  Revision-A boards are now available.	2005
3A	60-100W Hi-Fi Power Amp	Updated version of Project 03.  Capable of up to 100W into 4 or 8 ohms (with different supply voltages), this amp should satisfy nearly everyone.  It has excellent performance, is easy to build, and is a very solid and reliable amplifier.  One of the most popular ESP projects.	2009
3B	25W Class-A Hi-Fi Power Amp	A modified/updated version of Project 3A.  Capable of around 25W into 8 ohms, this amp should satisfy those who prefer the idea of a Class-A approach to audio.	2004
53	Output Power Limiter	Just the thing for hire equipment, or if you want to limit the amplifier power to stop the kids from blowing up your speakers.  A simple limiter that can be set to the required power with a trimpot, and no amount of overdrive will exceed the preset power limit.	2000
56	Variable Impedance	The DoZ project promised the ability to vary the output impedance of the amp, but this is applicable to any amplifier.  Here are the details.  Is it trivial - NO! Is it worth the effort? ABSOLUTELY.  You will never know the possible benefits (or otherwise) until you try it.	2012
68	300W 500W Subwoofer Amplifier	By far the biggest (serious) power amp I have published, this amp is designed especially for subwoofers, and is ideally suited for electronically equalised systems	2007
72	20W/Ch  Stereo IC amplifier	Based on the versatile LM1875 from National Semiconductor, this amp is ideal for PC speakers, surround sound, or tweeter amps in triamped systems.	2013
76	Opamp Based Power Amplifier	This is a contributed project, and has some interest value - especially as a learning exercise.  It is simple to build, and will make a good first project.	2017
83	MOSFET Follower Power Amplifier	Another contributed project that will be of great interest to those who value simplicity and good performance.  Like Project 76, it is simple to build, and will make an excellent first project.	2016
101	MOSFET Power Amp	This MOSFET power amp has the highest performance of any similar design I have tested, with vanishingly low distortion and wide bandwidth.  It is also simpler than most, but lacks nothing as a result.	2001
114	Class-D Amplifier	Complete details for building a stereo (or even a multi-channel) amp or subwoofer amp, using the new ColdAmp BP4078 Class-D amplifier modules.	2005
115	GainClone Amplifier	This article is in two parts, and describes with photos and drawings how to build a very nice looking GainClone chassis.  Using the P19 and (optionally) P88 +P05 boards.	2006
116	Class-D Subwoofer amp	This describes a complete 'plate' amplifier for subwoofers.  Using the P84 equaliser, and either P48 or P71 sub-resonance sub controller.  Power is from a ColdAmp BP4078 Class-D amplifier module.  These modules are no longer available.	2006
117	1.5kW Power Amp	Insanity! This project is designed specifically for those who think that one can never have too much power.  Hopefully, after reading this, the constant requests for more power will stop.  It is capable of destroying any loudspeaker connected to it, regardless of claimed power rating.	2006
120	Crowbar Protection	A crowbar loudspeaker protection circuit is the last resort, but if it saves an expensive loudspeaker it will have paid for itself many times over.	2007
127	TDA7293 Power Amp	A simple to build dual channel power amp, using the TDA7293 Power Opamp ICs.  The board for this is very small, making it easy to fit into tight spaces if necessary.	2009
137	Powered Box Amplifier	A complete preamp, crossover and power amplifiers, designed for powered PA speakers.  Can also be used to replace the amp in Leslie cabinets, 'party' systems, etc. (Note: 3 Part article)	2019
169	Battery Powered Amplifier	There seems to be some mystique about amplifiers that don't connect to the mains, and are therefore considered (at least by some) to be more 'pure'.  However, you don't need to shell out a fortune	2016
175	BTL Amp DC Protection	Single Supply BTL (bridge tied load) amplifier speaker protection circuit, used when P33 cannot be used due to the amp's DC Offset.	2017
178	Low Voltage Power Amplifier	Techniques you can use to build a low-power, low voltage power amplifier.  Ideally, it should have much better performance than the common LM386 and its ilk.	2018
180	Amplifier 'Power Meter'	Add this meter to your power amplifier for some bling that (unlike most) is not simple 'eye candy', but actually shows how close you are to clipping	2018
186	Workbench Amplifier	Single Chip 25 Watt/ 8 Ohm Workbench Power Amplifier.  Ideal for testing speakers, signal tracing, testing preamplifiers and a host of other uses	2019
208	Speaker box DC Protection	Stand-alone DC protection circuit for speaker enclosures.  Don't want some random amplifier failure to kill your expensive speakers?  This circuit should provide some peace of mind.	2020
216	Speaker Emulation Load	A Reactive Dummy Load For Testing Amplifiers.  Verify that your amplifier(s) don't have protection circuit 'artifacts' when subjected to a reactive load	2021
217	Low Power Amplifier	This is classified as a 'practice' amplifier, as it allows the reader to practice construction of an amplifier, and learn how amps work.  It uses low cost parts throughout.	2021
240	10 Watt Audio Amp/ DC Supply	A single-supply bench amplifier that can be used as a source/ sink power supply at up to 500mA.  Ideal as a basic amplifier or battery charge/ discharge unit.	2023
243	'Retro' Hi-Fi System	There are some people who like the idea of a retro hi-fi system, but can't find (or afford) the genuine article and/ or the cost of bringing it back to factory specs.  This project is based on the Sansui AU-555A integrated amplifier.	Aug23
No.	Headphone Amplifiers/ Adapters	Description	Date	Flags
24	Hi-Fi Headphone Amplifier	Contributed by a reader, this is a very nice circuit - enjoy the best of headphone performance
70	DoZ Headphone Amplifier	The DoZ is a nice little amp, and it occurred to me that it is ideally suited to headphone use.  Using smaller power transistors (and a much smaller heatsink), the performance into headphones is outstanding.  Revision-A PCBs are now available.	2005
100	Headphone Adaptor	This adaptor is intended to provide a headphone output for power amplifiers not so equipped.  It is very simple, and is easily adapted to amplifiers of almost any power.	2003
109	Portable Headphone Amp	This contributed project features crossfeed, and is designed for portable use.  It can naturally be used as a mains powered unit as well, and should satisfy most headphone users.	2005
113	Hi-Fi Headphone Amp	Although there are several other headphone amps, this one is very nice, very flexible, and PCBs are available.  It performs extremely well indeed.  It is easily adapted to use crossfeed (as a front-end add-on), and runs from a regulated supply for lowest noise	2005
No.	Preamps & Accessories	Description	Date	Flags
02	Simple High Quality Hi-Fi Preamp	As it says - simple, high quality preamp.  Has all the facilities normally expected, and is easily modified to your own requirements.  Note: This project is now superseded by Project 88 (but this is still worth reading).	2000
06	Phono (RIAA) Preamp	Very high quality moving magnet phono preamp - few circuits will better this one.  Performance is excellent (also, see P187 below if you use a moving coil cartridge)	2013
25	Phono Preamps For All	Circuits for moving coil and moving magnet pickups, a range of different equalisation circuits and a complete explanation of RIAA equalisation
32	Car Audio Preamp + Artificial Earth	Especially for car audio installations.  Includes some basic ideas on how to use the artificial earth on other conventional) audio circuits
37	Death of Zen Preamp	"Minimalist" preamp, with excellent specifications, designed to suit the DoZ (or any other) power amplifier.  (see P37-A for latest version)	1999
37-A	Death of Zen Preamp (Rev A)	Updated version of the 'minimalist' preamp, now uses dual supply rails (use P05 power supply).	2007
51	Balanced Line Drivers	Use these to eliminate hum for long signal leads, or when you cannot eliminate that &*&$$# hum loop from your system	2000
80	Reverse RIAA Equaliser	Do you have an unused phono input?  With this little contributed project, you can use it for any other signal source, or you can test phono preamps for correct equalisation.	2001
87	Balanced Line Drivers II	Some more examples of balanced line transmitters and receivers, with higher performance than those in Project 51.  Don't forget to check out the section "Hey! That's Cheating" - you may be surprised at the findings on this method.	2002
88	High Quality Audio Preamp - Mk II	Project 02 is pretty much past its use-by date now, so I figured it was time for an update.  This new version has PCBs available, and its performance is as good or better than the best commercial offerings around.  Very flexible design, so the board can be used anywhere a preamplifier is needed.	2002
91	78 RPM and RIAA Phono Preamp	There is a distinct lack of professional DIY phono preamps that are capable of working with the vast number of different standards that were used for 78 rpm recordings.  This project is based on the P06 preamp (and can use the same PCB), and will give results that are second to none	2002
97	Hi-Fi Preamp	Unlike most of my projects, this was designed from the PCB backwards.  It is intended for use with PCB mounted pots, and provides Bass, Treble, Balance and Volume controls.  A completely new technique for de-sensitising the tone controls gives you full range or very restricted control for minor corrections.	2008
99	Subsonic / Rumble Filter - Rev-B Boards	A conventional but very effective filter to remove extraneous subsonic noise from vinyl disks, either for listening or transcription to CD.  A very steep 36dB/octave filter removes frequencies below 17Hz.	2009
104	Preamp/ Crossover Muting Circuit	A useful addition to any crossover or preamp project that insists on making rude noises - typically just after power is turned off.  May be expanded to as many channels as needed, and uses readily available parts.	2004
107	Phase / Polarity Switch	Simple switching circuits to allow normal or inverted polarity of the signal.  May be used to experiment with the concept of 'absolute phase', or anywhere else that a switched polarity reversal circuit may be useful.	2004
110	IR Remote Control	Something that readers have been asking for has finally arrived - a complete (simple but functional) infrared remote control for preamps.  It provides a driver for a motorised pot for volume and a relay for mute, and short-form kits are available	2004
141	VCA Based Preamplifier	If you need a multi-channel preamp with a single volume control for all, this might be just what you're looking for.  Ideal for home theatre! You can have from 2 to 8 channels, or even more if needed.  Uses the THAT2180 VCA chip for excellent performance	2013
163	Preamp Input Switching Using Relays	How to use relays for input switching, including several designs for logic controls to allow push-button input selection	2016
167	MOSFET Follower & Circuit Protection	Many people like their valve (tube) preamps, but if connected to opamp circuits the voltage 'surge' at power-on may cause damage.  A MOSFET follower and a muting circuit are also provided.	2016
171	Infrasound Translator	Infrasound (between 1Hz and 20Hz) is normally inaudible, but this project allows the sound to be heard by using a voltage controlled oscillator to move the low frequencies to the audible range.	2016
176	Fully Differential Amplifier	P87A & B have been around for years, but sometimes you need the best possible common mode rejection ratio (CMRR).  This circuit does just that.	2018
187	Moving Coil Head Amp	The P06 phono preamp has been the 'go-to' design for a vast number of people since published, but a moving coil preamp wasn't something I wanted to tackle.  That's now changed, and the designs presented will out-perform most discrete circuits.  Includes a discussion of noise and low noise circuitry.	2019
188	Surround Sound Decoder (Mk. II)	While Project 18 shows a surround sound decoder, this one is far more complete, and uses readily available PCBs supplied by ESP.  It's in operation, and works very well indeed.  It includes the subtraction circuit, digital delay (Project 26A) and a balanced output that provides the out-of-phase signals for the surround speakers.	2019
194	Withdrawn	N/A
199	ABC NYE EQ	ABC New Years Eve Concert Equaliser (Specific To Australia, but ...)  End the muffled sound broadcast by the ABC!	2020
202	Piezo Preamplifiers	Piezo guitar/ violin/ double bass etc. pickups are common, and I figured it was time to provide a few options.  Includes one of the lesser known types - a charge amplifier (includes ceramic phono pickups)	2020
226	Versatile Tone Controls	A variable tone-control circuit that offers greater flexibility than most.  Includes options to use it for musical instruments (especially guitar/ bass).  Unlike most, it can be adapted to provide 12dB/ octave slopes instead of the 'standard' 6dB/ octave types you're used to using.	2022
235	Current Feedback Opamp	Current feedback (CFB) opamps are much faster than anything you're used to.  This is a DIY (fully discrete) circuit you can use to look at the capabilities of these devices.	2023
243	'Retro' Hi-Fi System	There are some people who like the idea of a retro hi-fi system, but can't find (or afford) the genuine article and/ or the cost of bringing it back to factory specs.  This project is based on the Sansui AU-555A integrated amplifier.	Aug23
246	Clipping Indicator	A clipping indicator that can be set for preamps or power amps.  It will also work with single supply BTL amps with one external capacitor.	Dec23
247	Tape Head Preamp	This is best described as an experimental circuit, since I don't have a tape deck and can't test it.  Using the P06 Phono preamp board, it provides NAB and IEC EQ for 7½ & 15 ips.	Dec23
No.	Crossovers, Filters & Effects	Description	Date	Flags
08	2-Way Electronic Crossover	Conventional 3rd order electronic crossover	1999
09	24dB/Octave 2/3-Way Xover	Linkwitz-Riley alignment and phase coherent !!  This is an extraordinarily nice crossover, and is suited to top of the line hi-fi or professional installations	2007
18	Simple Surround Sound Decoder	Line-level active and passive versions of the 'Hafler matrix' decoder	1999
21	Stereo Width Controllers	Two to choose from.  Expand or contract the stereo sound stage	1999
26	Digital Delay Unit	Digital delay, and all the info to construct a complete surround system (Note - The delay IC no longer available)	2012
26A	Digital Delay Unit	Digital delay, based on the popular PT2399 IC.  A very flexible unit with many applications.	2012
28	Parametric / Sub-Woofer Equaliser	A simplified version, which performs surprisingly well and has more options than most of the more complicated circuits	2006
48	Sub Woofer Processor	Using the ELF™ "Extended Low Frequency" principle, this processor is designed to operate a sub-woofer driver below its resonant frequency.  This means that the box is small, resonance can be (comparatively) high, and the load is completely predictable	2004
48A	Sub Woofer Processor, Revision A	Operates much like the original P48 (above), this new version of the P48 processor is designed to operate a sub-woofer driver below its resonant frequency.  The latest version is far more flexible than the original.  (Created 12 Jan 2009)	2009
63	Multiple Feedback Bandpass Filter	This is the basis of the expandable equaliser and analyser mentioned below as up and coming projects.  Marginally useful in its own right, it is the ideal building block for these projects, and can also be used to build a vocoder!	2000
67	Fast Audio Peak Limiter	This peak limiter is simple and very effective.  Using a discrete FET as the gain control element gives low distortion and very fast response times.	2000
71	Linkwitz Transform Circuit	The Linkwitz Transform circuit is an equaliser to provide extended bass response from any loudspeaker in a sealed enclosure.  The effect is similar to the EAS equaliser described in Project 48, but the range is no longer only below resonance, but encompasses the normal frequency range of the driver.	2000
75	Constant Q Graphic Equaliser	This is a novel constant Q design, that allows the maximum boost and cut to be varied with a single pot.  This project can be made using as many or as few sections as you need.	2001
78	3-Way 12dB/ Octave Crossover	This is a contributed project, and describes a simple high performance 12dB/ Octave crossover network	2001
81	12dB/Octave 2-Way Xover	Linkwitz-Riley alignment and phase coherent - another very nice crossover where 24dB/ octave is not needed (this uses the P09 PCB, with only a few additional wire links - no tracks to cut)	2007
84	Subwoofer Graphic Equaliser	This is a constant Q design, with eight 1/3 octave bands covering 20Hz to 100Hz.  With up to 14dB boost and cut, even the most recalcitrant subwoofer installation will be brought into line, ensuring the best possible performance.	2009
103	Subwoofer Phase Controller	A standard phase control circuit.  Nothing extraordinary about this project, but after many requests I have finally added it to the list.	2012
123	18dB/Octave Crossover	A small collection of ideas for building an active 18dB/ Octave crossover network.  Includes a scheme for a 'quick and dirty' version that gives a good result for the lowest cost	2009
125	4-Way 24dB/Octave Crossover	A complete 4-way Linkwitz-Riley crossover, with balanced input stage, individual level controls, on-board regulators and output buffers.  15 Oct 2009	2009
148	State Variable Crossover	Perfect for loudspeaker system development, or can be used as part of a biamped or triamped system.  12dB/octave continuously variable filters.	2014
155	Variable High And Low Pass Filters	These circuits are common in mixing consoles, but you might find them useful elsewhere as well.  The frequency ranges can be adjusted to suit your needs.	2015
170	6dB/ Octave Active Crossover	Some people like the idea of 6dB crossover networks.  While first order networks provide little by way of driver isolation, there might be a few readers who'd like to experiment	2016
218	High Q Gyrator Filter	A number of ESP projects have used gyrators, but the one described here is different.  It can be made to have a very high Q, providing a very sharp filter response.
253	18dB/ Octave State-Variable Xover	18dB/ Octave active crossovers are fairly uncommon.  This one uses a state-variable filter, and is more unusual than most.  The performance is very good, and it has some surprising benefits.	2024
254	24/ 18dB/ Octave Asymmetrical Xover	An asymmetrical crossover can provide a useful difference in group delay, allowing you to time align drivers without having to use a phase-shift network or stepped baffle	Sep24
No.	Equalisers	Description	Date	Flags
28	Parametric / Sub-Woofer Equaliser	A simplified version, which performs surprisingly well and has more options than most of the more complicated circuits	2006
48	Sub Woofer Processor	Using the ELF™ "Extended Low Frequency" principle, this processor is designed to operate a sub-woofer driver below its resonant frequency.  This means that the box is small, resonance can be (comparatively) high, and the load is completely predictable	2004
63	Multiple Feedback Bandpass Filter	This is the basis of the expandable equaliser and analyser mentioned below as up and coming projects.  Marginally useful in its own right, it is the ideal building block for these projects, and can also be used to build a vocoder!	2000
64	Instrument Graphic Equaliser	Designed especially as a guitar / bass equaliser, this unit is expandable, and is really a multi-section (23 as shown) tone control.  Offering a wide tonal range and great flexibility, it can be adapted to any musical instrument.	2000
75	Constant Q Graphic Equaliser	This is a novel constant Q design, that allows the maximum boost and cut to be varied with a single pot.  This project can be made using as many or as few sections as you need.	2001
84	Subwoofer Graphic Equaliser	This is a constant Q design, with eight 1/3 octave bands covering 20Hz to 100Hz.  With up to 14dB boost and cut, even the most recalcitrant subwoofer installation will be brought into line, ensuring the best possible performance.	2009
149	Musical Instrument Graphic EQ	Guitar, Bass or Keyboard Equaliser.  A greatly improved version of Project 64	2014
150	Wien Bridge Based Parametric Equaliser	A building block that can be used in mixers, preamps, guitar and bass amps, etc.	2014
153	Frequency 'Isolator' EQ	'Isolator' EQ is very common amongst the DJ fraternity, but they can be rather expensive.  Now you can build your own, and with all the features you need	2014
173	Constant Directivity Horn Equalisation	Constant directivity (CD) horns are unique amongst high frequency reproducers.  They need a 6dB/ octave boost for high frequencies, as provided by this project	2017
197	Low Frequency Boost & High Pass Filter	If you need to equalise a vented speaker enclosure, this low frequency boost and high pass filter circuit may be just what you need.	2019
199	ABC NYE EQ	ABC New Years Eve Concert Equaliser (Specific To Australia, but ...)  End the muffled sound broadcast by the ABC!	2020
No.	Power Supplies	Description	Date	Flags
04	Dual Power Supply	A power supply that is suitable for most amps of 60W output.  Can be adapted or modified to other voltages for more or less power
05	Updated Preamplifier Power Supply	All the features of the earlier versions with an improved muting circuit.  Revision-D PCB.	2007
05-Mini	Budget Preamplifier Power Supply	A simple dual power supply using fixed regulators.	2018
15	Capacitance Multiplier Supply	For Class-A Amps - Extremely low ripple power supply with much less power dissipation than a regulator	2001
38	Signal Detecting Auto Power-On Unit	When you have a sub-woofer or other equipment that needs to be turned on with the main amp, this is the answer.  Detects signal and applies power.	1999
39	Soft Start Circuit	Designed for power amps using (large) toroidal transformers, this will limit the inrush current to a sensible value.  A PCB is now available for this project, using a new circuit (shown on the project page).	2006
40	Load Sensing Auto Switch	How to apply power to the entire audio system by turning on one item (typically the preamp).  Note that this version is superseded by Project 79.
43	Ultra Simple Split DC Supply	When you need a +/- supply, and only have a DC adapter, this little project might just be what you need	1999
44	Dual +/-25V Lab Supply	Ideal for testing your latest creation, as the voltage can be advanced slowly to ensure that everything works as it should before 'real' power is applied.  Up to 800mA (typical) output current.
69	12V Switching Supply	Ideal for low power applications (such as equalisers or crossovers) in cars, where a +/-12V supply is needed.  This project is a perfect starting point for anyone thinking of building a high power switching supply, as it teaches the basics without the risk of expensive things blowing up.	2002
77	13.8V Power Supply / Charger	A power supply for testing and working on car amplifiers, this unit can be scaled up to about 500 Amps! Easy to build, and ideal for powering any car amplifier for test or service.	2003
79	Current Sense Auto Power Switch	A current sensing switch allows you to turn on multiple devices, just by turning on one master.  Use it to activate the entire Hi-Fi by turning on the preamp, or turn on all your PC peripherals when you turn on the computer.	2001
89	Car Switchmode Supply	The little supply (P69) has been here for a while, and here's the big one.  This supply is good for up to about 350 Watts, although I suggest that a more modest power of around 250 W is more appropriate for the most part.  High current and fully configurable to do what you want.  Do not attempt to build this without adequate test equipment or experience.	2002
95	Low Power Switchmode Supply	This little supply is designed to provide a negative voltage only, allowing you to use the car supply for the positive supply.  Current is only about 20mA, but this will be enough to properly power many car audio projects	2002
98	Automatic Charger for Battery Hi-Fi	Quite a few people like to use a battery supply for preamps especially, since the DC is completely smooth, and batteries are essentially noise free.  Unfortunately, they also need to be charged, and this project is designed to disconnect the charger automatically when the preamp is switched on, and re-connect it when the preamp is turned off.	2003
102	Simple Pre-Regulator	A great many constructors would like to be able to use P05 (Preamp Power Supply) from the main power amp supply, but the voltage is usually much too high.  Resistors may be used to drop the voltage, but these must be calculated, and will not allow for any additional load.  Using a pre-regulator allows you to reduce the voltage safely, and also provides a significant level of initial hum reduction.	2003
108	Switchmode PSU Protection	Switchmode supplies are common, but most have no form of protection - especially home made types or many of the cheaper car amplifiers.  This contributed project will add protection for over-voltage, under-voltage or high temperatures, and is cheap and easy to build.	2004
118	PC Peripheral Switch	This ultra simple project uses only a modified power board and a small wiring loom in the PC.  By using the PC's 12V supply, it is ultra reliable and cannot false trigger.	2006
138	Mains Under/ Over Voltage Protection	This project senses if the mains voltage falls below or rises above a preset threshold.  Designed to protect equipment from extreme mains voltage variations.	2012
142	Simple High Current Regulator	There are some instances where 3-terminal regulators just can't do what you need.  This can be due to higher than allowable input voltage or the need for more current than they can provide.  This regulator doesn't come with great specifications, but will be more than acceptable for many tasks.	2013
144	Mains Power Sequencer	If you need to turn on/off mains equipment in a preset sequence, this project will be just what you are looking for.  Suitable for large PA systems, recording studios, lighting, etc.	2013
151	High Voltage DC Supply	If you want to experiment with valve ('tube') circuits, you need a power supply for the B+ and DC for the heaters.	2014
156	12V Trigger Switches	Many home theatre receivers (aka audio-visual receivers or 'AVRs') have a 12V trigger output, and the circuits shown can be used to switch on equipment when the trigger voltage is present.	2015
184	Li-Ion Battery Cutoff	Li-Ion batteries are ideal for many projects (especially test equipment), and this project lets you ensure that the battery is not over-discharged if/ when you forget to turn it off.	2019
192	12V to ±12V Switchmode Supply	If you use a single 12V DC wall supply, that's often not enough to run many projects.  This supply gives you ±12V from the single supply from the 'wall wart'.	2019
193	12V to P48 Phantom Power Supply	Getting a suitable transformer for a P48 phantom supply isn't always easy, but this switchmode boost regulator can provide +48V from a single DC supply of 12-36V	2019
196	12V Float-Charge Battery Supply	This project is basically a 12V version of Project 98, and a 12V battery backup system is useful for electronic clock drives, or surveillance equipment.	2019
207	High-Current AC Source	If you need to run tests on very low resistances, this is ideal.  With up to 100A output current (intermittent), you can test things that are otherwise impossible.	2020
220	Low-Current Buck Converter	A tiny switchmode buck converter, to reduce up to +40V DC to the voltage you need.  It's only low current (around 100mA), but will be more than enough for many simple projects.  It's also ideal to reduce higher voltages with minimal losses to a lower voltage suited to a linear regulator for minimum noise.	2020
221	Tweeter Amp Regulator	If you really don't want your tweeter amp running from ±35V or more (~70W into 8Ω), use this regulator to reduce the voltage to something 'sensible', such as ±22V.  It can be use with main supplies up to ±56V, and provides the tweeter amp with a low ripple regulated voltage.  It includes (very) basic current limiting.	2021
222	Mains Soft Start Circuit	Designed for power amps using (large) toroidal transformers, this will limit the inrush current to a sensible value.    Unlike P39, this version doesn't use a transformer, so everything is at mains potential.  It's included for completeness, not because I think it's a good idea!	2021
223	Bench Power Supply	I've resisted publishing a bench supply, but after my old unit needed a major service I built one, and shared the details here.  Unlike P44, this unit uses dedicated circuitry, with many options, such as series/ parallel operation, your choice of meters, etc., etc.	2022
224	External In-Line Soft Start	This is (as near as I can tell) a unique project.  It's permanently connected to the mains, and it operates when you turn on your amplifier (or other load).  This will limit the inrush current, and it bypasses the limiting (thermistors or resistors) after ~300ms.	2022
233	Isolated Power DC-DC Supplies	A collection of ideas to provide a galvanically isolated power supply.  They are low-power, but most can provide enough current for a couple of opamps or to switch the gates of MOSFETs.	2022
238	Low Current HV DC	It's not every day that you need a high-voltage, low current DC source, but when you need one it's easy to build.  Several options are available, with an isolated output up to 500V or more.	May23
239	Signal Detecting Power-On Unit Mk II	When you have a sub-woofer or other equipment that needs to be turned on with the main amp, this is the answer.  Detects signal and applies power.  This revised circuit is designed to overcome an 'endless loop' of power-on/ off with some amplifiers (notably some Hypex amps).	2023
240	10 Watt Audio Amp/ DC Supply	A single-supply bench amplifier that can be used as a source/ sink power supply at up to 500mA.  Ideal as a basic amplifier or battery charge/ discharge unit.	2023
248	Low Voltage Charge-Pumps	Many times you'll need a low current voltage booster or inverter (to get a -Ve supply from a single +Ve supply).  The details here should help.	2024
No.	Musical Instrument	Description	Date	Flags
27	100 Watt Guitar Amp (Mk II)	The new and improved version of the original Project 27 guitar amp.  You still need the old material for the cabinet details and such, but the new description and schematics are all here.  Preamp (P27B) has been revised, and is now Rev-A.	2013
27 (old)	100 Watt Guitar Amplifier	The original of the unit above.  Retained for posterity, and has the speaker box details (may still be needed for the new version).	2004
29	Tremolo Unit	A versatile guitar effect.  This is a simple circuit that gives very good results
34	Guitar Spring Reverb Unit	A spring reverb unit for guitar amps
45	Simple Bass Guitar Compressor	An ultra simple compressor, ideally suited for bass guitar.  Very simple, but it works very well, and has that really 'chunky' sound that many bassists like - one for the experimenter, and really easy to fool about with.  Can be used with 'ordinary' guitar, too.
49	Guitar Vibrato Unit	A reasonably simple circuit, with results similar to the famous Vox AC30 guitar amp.  Also has a unique Effect control, allowing some interesting sounds.
64	Instrument Graphic Equaliser	Designed especially as a guitar / bass equaliser, this unit is expandable, and is really a multi-section (23 as shown) tone control.  Offering a wide tonal range and great flexibility, it can be adapted to any musical instrument.	2004
92	Guitar and Bass Sustain Unit	A compressor/ Limiter for guitar, bass or recorded music.  Uses a LED and LDR for low distortion control of the audio level.  See Project 145 for details on how to build a linear optocoupler.	2007
145	Silent Guitar Effects Switching	How to use Vactrol® or DIY optocouplers to switch signals in guitar amplifiers.  No contact bounce or clicks, just virtually silent switching without any noises.  Includes details of how you can build your own LED/ LDR optocoupler.	2013
152-1	Bass Guitar Preamplifier - Part 1	Part 1 of a very comprehensive bass preamp, with fully adjustable EQ, and all the bells and whistles! There is even the option to use a valve input stage for those who really think there's a difference.  There are also overload detection circuits that can be used as and where needed.	2015
152-2	Bass Guitar Preamplifier - Part 2	Part 2 covers the compression, effects send and return, tuner output and crossover networks for a biamplified bass rig, and a 'tweeter' crossover for those who want to add a horn to get a biting top end.  Also describes the soft-clipping circuits.	2015
162	Voltage Controlled Oscillator	A voltage controlled oscillator (VCO) isn't something you need every day, and you may never have thought that you need one.  You'd probably be right, but some things are just too interesting to ignore.	2016
195	Guitar 'Talk Box'	The guitar 'talk box' has been around for a long time, and it was made famous by many musicians in the 1970s.  It's still popular, and you can build your own.	2019
202	Piezo Preamplifiers	Piezo guitar/ violin/ double bass etc. pickups are common, and I figured it was time to provide a few options.  Includes one of the lesser known types - a charge amplifier.	2020
203	Guitar/ Studio Spring Reverb Unit	A complete spring reverb sub-system for guitar, keyboards or studio use.  Possibly the most complete reverb system currently available.	2020	PCB Pending
206	Guitar Vibrato Unit	An update on the original Project 49 unit, but using LED/ LDR optocouplers to allow high level audio without distortion.	2020
211	Guitar Spring Reverb Unit	Using the P113 headphone amp PCB, this spring reverb unit is for guitar amps or studio use.  Very high performance, and the PCB is available now.	2020
214	'Zero Capacitance' Guitar Lead	If you have problems losing 'tone' when the volume control on your guitar is turned down, this project will maintain full frequency response with almost any source impedance.	2020
215	P215-P27 Revisited Guitar Amp	The Project 27 guitar amp has been around since 1999, but this is a low-power version, more suited to most players today.  Nominal power is 40W, but it can be reduced to 20W by using an 8Ω speaker.  P27 PCBs (preamp and power amp) are used, and all changes are shown clearly.	2021
219	Valve Amp Speaker Switch	Speaker switches for transistor amps are easy, since they don't care if the output is open-circuit during the change-over.  Valve (vacuum tube) amps are different, and they may be damaged unless the switching uses make-before-break circuitry.  That's what's provided by this project (and it can be switched to use transistors amps as well).	2021
229	Enhanced Reverb Mute System	Most reverb systems mute the output, which stops reverb noise when it's off, but it also kills the 'tail' as the reverb decays.  By using an instant input mute and a delayed output mute, you can retain the reverb's natural decay, but prevent noise after the delay times out.  Uses an LED/LDR optocoupler for a smooth decay.	2022
249	Guitar Booster Circuits	A collection of circuits that can be mixed and matched for guitar/ bass boosters with or without additional equalisation.  Includes JFET, transistor and opamp designs.  These are for experimentation, and are not 'projects' in the strict sense of the term.	2024
252	6-Band Guitar EQ	A simple guitar equaliser circuit using simplified multiple feedback (MFB) bandpass filters.  Unlike most EQ circuits using these, there are only a few different component values.	May24	NEW
No.	Mixers, Meters, etc.	Description	Date	Flags
30	Stage and Recording Mixer	Able to be built in modular form, allowing as many (or few) channels as desired.  Includes effects sends, channel and master inserts, and 3-band EQ with tuneable mid.  This is the most ambitious project so far, in terms of overall complexity - not for the faint of heart !	2000
35	Direct Injection (DI) Box	An essential companion for the mixer for stage or recording work.  Includes high and low level inputs.  Two different versions to choose from - passive, or active 48V phantom / battery	2005
50	Mic Circuit Tester	This simple project was inspired by a reader, who needed a small oscillator to check mic circuits during sound setup.  It is fixed frequency (tuned to A-440), and provides from 0 to 100mV into a typical microphone input.	2000
55	PPM and VU Meter	A versatile and useful VU meter circuit, that can also operate as a Peak Programme Meter (PPM).  See the average and peak output level from an amplifier or preamp.  Can also be used with any mixer.	2006
60	LED VU Meter	Nothing even remotely special about this LED VU meter, but it is a useful project nonetheless.  Includes a simple rectifier circuit to allow full wave detection, and is suitable for line or speaker levels.	2008
94	Universal Preamp/ Mixer	A small preamp and mixer, able to be expanded into 4 stereo input channels.  Mic or phono preamps can be added to the front end to make a small and versatile home recording mixer.  Includes tone controls.	2005
94A	Universal Preamp/ Mixer	Alternative wiring scheme to get more inputs from a single board.  Includes tone controls.	2005
96	Phantom Feed Supply	Extremely low ripple and noise were the design goals, and this supply is extraordinarily quiet.  Using a simple discrete regulator means no hard-to-get high voltage regulators, and it uses a readily available power transformer as well.  Also features a phantom power microphone feed, and a technique to match supply resistors.	2005
128	VU Meter Bridge	Build a stereo analogue VU meter to monitor recording or live PA mix levels.  Uses the P87A PCB and is compatible with balanced and unbalanced systems.	2010
129	Matrix Mixer	Now you can build a matrix mixer to suit your exact requirements.  Uses the P94 Universal Preamp/Mixer PCB.	2010
135	Phase Correlation Meter	More of an experimental circuit than anything else, it should help anyone trying to build a phase meter.	2011
136	Real-Time Analyser	This hardware based real-time audio analyser is a contributed project, based on the multiple feedback bandpass filter described in Project 63	2011
146	Overload/ Clipping Indicator	Overload indicator for mixers, preamps or power amps.  Simple opamp comparator circuit gives fast response.	2013
183	Signal Detecting Audio Ducking Unit	Ducking is a common application for PA systems, video production or anywhere you need to reduce the level of a background signal in the presence of speech	2019
205	4-Channel Mixer	4-Channel Mixer For Microphones Or Instruments.  It's built using existing ESP boards (other than the clipping indicator which will be available at a later date).	2020
244	LED Level Indicator	A 3-LED level indicator for hi-fi, mixers, digitisers, etc.  Superseding the Project 60 LED meter, as the ICs are now obsolete.	Oct 23
No.	Digital Audio	Description	Date	Flags
85	Simple S/PDIF DAC	This is quite possibly the simplest possible S/PDIF receiver and DAC you will ever find.  Includes audio switching using relays, and for reference, TTL to COAX and COAX to TTL converter schematics are also available.[Contributed Project] Parts now obsolete!	2002
No.	Test Equipment	Description	Date	Flags
11	Pink Noise Generator	A very clean noise generator for loudspeaker and room acoustics testing	2011
16	Audio Millivoltmeter	For Testing Amplifiers (etc) - An analogue design, 3mV to 30V with dB scale (superseded by Project 236)	2006
17	A-Weighting filter	For noise measurements.  Ideal for use with the AC Millivoltmeter above	2002
22	Simple Audio Oscillator	For use with the millivoltmeter, for testing amps and speakers	2010
31	Full Featured Transistor Tester	Just the thing to check the transistors for any project	2005
41	Opamp Design + Test Board	This project will allow you to quickly assemble an opamp circuit for testing.  It is very easy and intuitive to use, and an indispensable tool for experimenters (4 opamps)	1999
52	Distortion Analyser	A simple distortion meter you can use with an oscilloscope or millivoltmeter, this project will allow reasonably accurate absolute measurements of THD + Noise (Total Harmonic Distortion), and very useful comparative measurements.	2007
58	Tone Burst Speaker Measurement Set	This project is based on work done by Siegfried Linkwitz (and is reproduced with his kind permission).  The project is in three parts - a cosine burst generator (don't worry, it will be explained), a microphone, and a calibrated peak detector.  With a suitable audio oscillator, complex and accurate speaker measurements may be made.  This is a fairly complex project, and uses a combination of analogue and digital ICs.	2008
59	Self Oscillating Amplifier	Excuse me??  No, it is not April!  Based on a idea from a reader, this project allows you to make a power amp oscillate at a defined frequency, eliminating the need for a low distortion oscillator for distortion measurements.  Includes a simplified distortion analyser circuit to suit.	2000
74	Simple RF Probe	This simple circuit is indispensable for any RF work.  Using just 4 passive components, it uses your multimeter as the measurement display.	2001
82	Loudspeaker Test Box	A very simple project that allows you to quickly and accurately determine the optimal impedance correction network across a loudspeaker, to ensure that the crossover actually works as you intended.  It also allows you to measure impedance.	2001
86	Miniature Test Oscillator	MiniOsc - A high performance test oscillator, with both sine and square wave outputs.  Ideal for bench or portable use, and has low distortion (<0.2%) and a battery drain of less than 2mA from a single 9V battery.	2010
106	hFE Tester for Transistors	An hFE tester with switched collector currents for the Device Under Test, covering a range suitable for the selection and matching of output transistors for amplifiers such as the JLH Class-A, ESP DoZ etc.  (contributed project)	2004
119	Component Signature Analyser	Test components while still installed in a circuit - component signature analysis is an easy way to find faulty parts, especially if you have a working circuit for comparison.  Features dual voltage and current ranges, and connects to your oscilloscope (in X-Y mode) to show a graphical indication of the circuit node.	2006
121	Inductance Adapter	Measure inductance for crossover coils using your multimeter or a frequency counter.  Several variations for you to experiment with and end up with a useful tool.	2008
124	High Power Dummy Load	A dummy load for testing amplifiers (and optionally power supplies).  In the full version, it offers impedances from 1 ohm to 16 ohms, with a free-air power rating of up to 360W.  This can be extended easily by using cooling as described in the article.	2009
130	Reverse A-Weighting	This is an odd one - I'm convinced that there's a need for a filter/ amplifier that reverses the A-Weighting curve, but I can't actually figure out what that need might be.  Still, if you need one, here it is.	2010
139	Mains Current Monitor	A versatile, safe and accurate way to measure (and view with an oscilloscope) the mains current drawn by mains powered equipment.  This project would appear to be unique - you can't buy a device that does this, but you'll wonder how you survived without it after making one.	2012
140	True RMS Adaptor	The only way to measure non-sinusoidal waveforms is true RMS or errors can be significant.  Use this adaptor to get true RMS readings.	2012
143	Tone Burst Generator/ Gate	There aren't many tone-burst generator projects on the Net, and sometimes no other piece of test gear will allow you to run the tests you need.  Check amplifier overload recovery, perform non destructive high power speaker tests, plus many more.	2013
154	PC Oscilloscope Interface	PC sound card oscilloscopes can be handy, but you need this circuit to make sure that it doesn't get blown up if you connect it to more than a few volts	2015
158	Low Noise Test Preamplifier	Every so often, you find that you need to listen to or measure signals that are well below the noise floor of your bench amp or 'scope.  With 20, 40 & 60dB of gain, this is what you need.	2015
164	Signal Tracer for fault-finding	A version of this project was shown in the troubleshooting pages, but it's now a project in its own right.  The unit presented here is simple, cheap, and runs from a 9V battery so it can be used almost anywhere.	2016
165	Valve Tester for Service Techs	If you service valve (tube) amplifiers, you need to be able to test valves under the conditions they are operated under in the amp being fixed.  This tester is designed to do just that, but it is not a 'general purpose tester.	2016
168	Low Ohms Meter	Most people don't need to be able to measure down to 10 milliohms or so, but sometimes there is a genuine need to do so.  This project shows how it's done.	2017
171	Infrasound Translator	Infrasound (between 1Hz and 20Hz) is normally inaudible, but this project allows the sound to be heard by using a voltage controlled oscillator to move the low frequencies to the audible range	2017
172	Wattmeter for AC Power Measurements	For all service and development work, it's useful to know the current drawn by the system, and it's also now easy to measure the power consumed.	2017
174	Ultra-Low Distortion Oscillator	Ultra-Low Distortion Sinewave Oscillator, a contributed project with both exceptionally low distortion and lightning-fast settling time	2017
177	Constant Current Transistor Tester	Test transistors using constant collector (actually emitter) current.  Ideal for matching small signal and power transistors (Bipolar types only).	2018
179	Sinewave Oscillator	A Filament Lamp Stabilised Wien Bridge Oscillator	2018
181	Accelerometer	Audio Accelerometer For Speaker Box Testing (amongst other things)	2018
182	Pseudo-Random Noise Generator	A maximum length sequence (MLS) noise generator with much better noise than a reverse-biased transistor junction (includes pink noise filter)	2019
185	Polarity Tester	Speaker, Microphone & Circuit Polarity Tester.  Ideal for checking that everything in a system is properly phased to prevent sound anomalies.  Can check microphones, speakers as well as mixers, preamps, power amps, etc.	2019
186	Workbench Amplifier	Single Chip 25 Watt/ 8 Ohm Workbench Power Amplifier.  Ideal for testing speakers, signal tracing, testing preamplifiers and a host of other uses	2019
189	Audio Wattmeter	Measure true power from an amplifier into a dummy load, or from an amplifier into a speaker.  Handles reactive loudspeaker loads and shows the actual power delivered.	2019
191	Peak Voltage & Current Detector	If you are unsure if your amplifier is way under or over-powered for your loudspeakers, this simple project can be used to monitor the peak voltage and current demanded while listening.	2019
207	High-Current AC Source	If you need to run tests on very low resistances, this is ideal.  With up to 100A output current (intermittent), you can test things that are otherwise impossible.	2020
209	Resistor/ Capacitor Decade Boxes	Resistance/ capacitance decade (or substitution) boxes can be handy.  There are three different circuits, so choose those you need.	2020
212	High Impedance DC Voltmeter	With an input resistance of 50MΩ or even 500MΩ you can measure voltages in very high impedance circuits.	2021
216	Speaker Emulation Load	A Reactive Dummy Load For Testing Amplifiers.  Verify that your amplifier(s) don't have protection circuit 'artifacts' when subjected to a reactive load	2021
225	Inrush Current Tester	Testing for worst-case inrush current isn't easy, but this mains switching unit allows repeatable results for transformer and electronic loads.  I expect that few people will need one, but if you do this is a low-cost and reliable option.	2022
228	Negative Impedance Test Amp	Driving transformers with negative impedance can increase performance dramatically.  This test amp lets you experiment with negative impedance to get the best result.  The effectiveness of negative impedance has to be experienced to be believed.	2022
230	Signal Routing Panel	Your workbench functionality can be greatly improved with this simple project.  It has inputs for a tuner and CD player, and you can switch between direct and via your latest project circuit.  It includes balanced inputs and outputs if you need them.	2022
232	Distortion Measurement System	Using an external PC sound card and some dedicated hardware, this system lets you measure distortion, noise and other system anomalies.  The full version described is 'over the top', but you can include the bits that you need.	2022
234	Resistor Substitution Box	Probably the simplest project I've published, this box uses a 10k, 10-turn pot and switched resistors to cover the range from ~100Ω to 100k (or 80k).	2022
236	AC Millivoltmeter	A new design for an AC millivoltmeter, covering the range from 300µV to 30V in 10dB steps.  This is a new design that supersedes P16 (that design is 24 yeas old now).	Feb23
237	JFET Test System	JFET circuits are always a bit tricky to design.  This tester automatically sets the bias voltage to get the same drain current for each JFET, making tests much easier.	Mar23
241	Z-Weighting Filter	Z-Weighting is 'flat' response, covering the audio band (20Hz to 20kHz).  The benefit is that all superfluous frequencies are removed, with a 12dB/ Octave filter for low frequencies, and 18dB/ Octave for HF.	Aug23
242	Cosine Burst Generator	A simplified version of the Project 58 cosine generator, designed by Siegfried Linkwitz and updated by Ray Hernan.  This uses a 10-cycle burst, which makes it easier to build.  Note that the circuit is 'experimental', and you may need to tweak a few values in the final version.	Aug23
250	Inductor Saturation Tester	Test the maximum current through any inductor, based on core saturation.  Requires the use of a digital scope using single sweep mode, but an analogue scope can be used if you have no choice.	Mar24	NEW
251	Protected DC Load	A DC load that includes protection against the preset power level from being exceeded at any voltage or current.  Uses an analogue multiplier to derive power.  Rated for 10A at up to 60V, bt not at the same time, because the multiplier will reduce the current as the voltage is increased.	Apr24	NEW
No.	Microphones and Mic Preamps	Description	Date	Flags
13	Low Noise Preamplifier	Simple unbalanced design, suitable for microphones - very low noise	1999
66	Low Noise Balanced Mic Preamp	A discrete front end makes this balanced microphone preamp very quiet, and it has excellent noise rejection.  Since the SSM2017 has been discontinued (sad but true), and if you can't get the INA217 this may be the ideal replacement	2008
93	Recording and Measurement Microphones	An introduction to microphones, as well as a variety of powering methods for electret capsules.  Phantom powered mic preamps, and more.	2008
112	Dummy Head Recording Microphone	Complete details on how to construct a dummy head recording mic.  Using either P93 or (surprisingly perhaps) P88 as the mic preamp, the performance is something to surprise you.  You will never know just how good a dummy head recording can be until you try it yourself.	2006
122	Simple Balanced Mic Preamp	This is a "utilitarian" preamp.  Although not intended where lowest noise is needed, it is still quiet enough for most applications, and will almost certainly be all that's needed for adding a microphone input to an amplifier or powered speaker.	2008
134	4mA Current Loop Microphone	This type of powered mic is quite common for professional measurement microphones, but is not well known outside the noise measurement field.  This project provides all the info you need to make your own 4mA current loop mic system.	2004
183	Signal Detecting Audio Ducking Unit	Ducking is a common application for PA systems, video production or anywhere you need to reduce the level of a background signal in the presence of speech.	2019
190	Microphone Muting Circuit	This simple project can be used to mute any microphone by the performer, including mics that are phantom powered.	2019
204	Frequency Shifter	Used for acoustic feedback reduction.  There's a choice of two circuits, one being an updated version of the first published frequency shifter (Wireless World, 1973), plus a contributed high-performance version that will have a PCB available (demand and COVID-19 permitting).	2020	Pending
No.	Miscellaneous Projects	Description	Date	Flags
01	A Better Volume Control	A volume control using a linear pot that is much better than most log pots.  Also a better balance control.	1999
07	Discrete Op-Amp	Class-A Output.  Intended as an experimental device, but it works extremely well	1999
231	Fast Discrete Op-Amp	Using 6 transistors, this opamp can provide 40dB of gain at up to 1MHz.  There are several options, and it's ideal for experimenters.  Very low distortion too.	2022
14	Power Amp Bridge Adapter	A conventional adapter for bridging power amplifiers	2007
20	Simplest Ever Bridge Adapter	Use this simple method, and avoid external circuits
42	Thermo-Fan For Amp Cooling	Use a 12V computer fan to keep your amp cool.  Uses a simple but very effective diode temperature sensor (Updated)	2002
46	Thermal Shutdown + Amp Thermal Protection	What happens if your amp gets too hot?  It will probably self destruct, or at least reduce the life of the power devices.  Add this circuit to either turn the amp off, or activate a cooling fan.  This is similar to one I use on my own system
54	Low Power FM Transmitter	Not really suited for "Bond, James Bond" spying activities, but will be useful to retransmit from the hi-if to another FM receiver nearby, or use it as a wireless microphone or guitar link.  Not in the same league as the commercial offerings, but much, much cheaper.	2002
57	SIM - The Simple Version	Ah!  The simple SIM must be a compromise, you say.  Well, actually the complex version is a compromise - this is the real thing.  The smallest variation in amplifier performance will create a signal that the SIM (Sound Impairment Monitor) can react to with startlingly accurate reactions to even the smallest variations in an amplifier.	2000
73	Hi-Fi PC Sound System	A Hi-Fi PC Speaker system? You have never heard your MP3 collection, CD or games sound so good.  If you could buy one, a system of this calibre would probably set you back more than the PC itself - The sound is very, very good!	2001
126	PWM Dimmer/Speed Control	This circuit is a versatile PWM controller for low voltage DC.  It can be used to control 12V LED lighting, DC motors, heaters, or anything else that responds to PWM current control.  The circuit uses readily available parts, and can even be controlled via C-BUS or other automation systems that support 0-10V control.	2009
131	Light Activated Switch	This has very little to do with audio, but I suppose that you could use it to switch on your hi-if (instead if a light) when it gets dark.  A versatile and easily configured light (or temperature) activated switch.	2010
132	Air Bearing Linear Tonearm	This is a submitted project, and it must be emphasised that it is to be used as a source for ideas for people with machining experience and equipment.  There is a considerable amount of work involved, and great scope for either wasting lots of bits of aluminium and other materials, or creating your own variation.  If you have the machines - highly recommended.	2010
133	PA-PC Audio Interfaces	If you need to interface from the output of a PC to PA system, or take a recording from the PA when the only thing available is a speaker line, this project shows you how to connect the PC and PA without damaging either.	2011
147	BJT Muting Switch	A little known technique that doesn't look like it could ever work - using bipolar transistors.	2013
171	Infrasound Translator	Infrasound (between 1Hz and 20Hz) is normally inaudible, but this project allows the sound to be heard by using a voltage controlled oscillator to move the low frequencies to the audible range.	2017
198	MOSFET Relay	MOSFET relay using Si8751/2 MOSFET driver ICs.  Suitable for mains switching (with caveats) or for high voltage speaker protection where a relay will arc.	2019
200	DIY LDR Optocoupler	Build your own 'Vactrol™' using a LED and LDR (light dependent resistor).  This has been 'transplanted' from an article where it was shown as part of construction project.	2020
210	AC and DC Electronic Fuses	Electronic fuses for AC or DC, with latching when a fault is detected.  Very fast acting, but can be slowed down if necessary.  Reliable protection for delicate electronics.	2020
213	DIY voltage controlled amplifier (VCA)	It's not hi-fi, but it is fun to build and play around with.  Using only common parts, it's ideal for 'utilitarian' applications, guitar tremolo, etc.	2021
227	Hybrid Relay	This was designed because the IC for the P198 MOSFET relay is not available.  It's a combination of a standard relay and a MOSFET relay, and is designed for loudspeaker protection.	2022
235	Current Feedback Opamp	Current feedback (CFB) opamps are much faster than anything you're used to.  This is a DIY (fully discrete) circuit you can use to look at the capabilities of these devices.	2023
245	MOSFET Relay	A new MOSFET relay, using the TI TPSI3052-Q1 IC.  This one can be used for high-speed switching, as well as a second-source for P198.  It's a very impressive IC!	Nov23
ABX	ABX Comparator	Building on the basic concept of Project X, this contributed project utilises the original techniques of a true ABX tester.  It can be made as a simple AB tester, or build the random remote for full ABX testing.	2002
X	A-B Switch Box	Yes folks, Project "X" has arrived (I just had to have one!).  This is a contributed article / project, and might be confronting to some who steadfastly maintain they can hear minute differences between amplifiers.  Now is your chance to prove it	2000
No.	Lighting Equipment	Description	Date	Flags
62	LX-800 Lighting Controller	Light is always needed for theatre and live music, and this is just the ticket.  This is an ambitious project, and requires considerable mains wiring - use extreme caution.  (Note - opens in a new window) Major Update!	2005
65	Strobe Light	Designed as a companion to the lighting controller, but can also be used by itself (or with any other lighting controller).	2006
90	Dimmer Control Voltage Reversal	Some older Strand dimmer units used a zero to -10V control signal, and the standard analogue control is zero to +10V.  This project allows the easy conversion from one standard to another	2002
157	3-Wire Trailing-Edge Dimmer	You can't buy these easily, so the only option is to build it yourself.  This is the first (and only) fully tested and working design you'll find anywhere.	2015
159	3-Wire Leading-Edge Dimmer	You can't buy these easily either, so again the only option is to build it yourself.  This is also the first (and only) fully tested and working design you'll find anywhere.	2015
201	Multi-Channel Trailing-Edge Dimmer	This project came about from the MOSFET relay (P198) and is suitable for use in the Project 62 'LX-800' dimmer, or used as a stand-alone system.	2020
245	MOSFET Relay	A new MOSFET relay, using the TI TPSI3052-Q1 IC.  This one can be used for high-speed switching (e.g. dimmers), as well as a second-source for P198.  It's a very impressive IC!	Nov23
No.	Loudspeaker EQ	Description	Date	Flags
48	P48 EAS Subwoofer & Controller	This has proven to be a very popular project since it was first introduced, and that interest has not waned.  Using the ELF™ "Extended Low Frequency" principle, this processor is designed to operate a sub-woofer driver below its resonant frequency.  This means that the box is small, resonance can be (comparatively) high, and the load is completely predictable.	2000
71	Linkwitz Transform Circuit	The Linkwitz Transform circuit is an equaliser to provide extended bass response from any loudspeaker in a sealed enclosure.  The effect is similar to the EAS equaliser described in Project 48, but the range is no longer only below resonance, but encompasses the normal frequency range of the driver.  Updated	2006
173	Constant Directivity Horn Equalisation	Constant directivity (CD) horns are unique amongst high frequency reproducers.  They need a 6dB/ octave boost for high frequencies, as provided by this project	2017
197	Low Frequency Boost & High Pass Filter	If you need to equalise a vented speaker enclosure, this low frequency boost and high pass filter circuit may be just what you need.	2019

Although I am happy to provide assistance to prospective builders, I cannot (and will not) be drawn into prolonged e-mail exchanges if the project does not work as expected.  I can say with complete confidence that all projects presented will work if properly constructed according to the published design.  This is not to say that no help will be available - I will always help where I can.

It is inevitable that in some cases (due to component tolerances, for example), a project may require a different value resistor, capacitor (or whatever) to correct for an unexpected variation.  Since I cannot control or predict the quality of components sourced by readers, nor the standard of workmanship in assembly, it is not possible to allow for every contingency.

Please do not attempt the construction of any project which you do not fully understand, or if you do not feel completely confident that you can build the project without further assistance.  Do not expect me to be able to diagnose an obscure fault remotely, and especially if the project has been modified in any way whatsoever.

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